This invention relates generally to controlled chemical oxidation or combustion of hazardous organics and other combustible waste materials. More particularly, the present invention pertains to a method and an apparatus for improving combustion of waste materials using a wet oxidation reactor in combination with various fuels and oxidants which facilitate and enhance the combustion of such waste materials.
Still further the present invention is directed to the incineration or combustion of combustible waste, such as hazardous wastes, industrial wastes, mixed hazardous radioactive wastes or radioactive wastes, which may comprise fine particulates, gaseous materials, organic solids and liquids ranging from low boiling materials to gummy organics with suspended solids. Such waste materials can include paint, paint stripping wastes, coatings, and spent cleaning solvents; liquid organic wastes from chemical plants or other chemical processing operations, such as hazardous waste chemicals, solvents, liquid polymers and polymer solutions, dispersions, emulsions, and chemical reaction byproducts; oil and sludges from petroleum refining operations, such as waste petroleum products, residues from distillation columns, and unrefined byproducts; from manufacturing operations, such as spent solvents and lubricants; from food processing operations, such as spent cooking oils and processing oils; from printing operations, such as inks and cleaning solvents; and the like. Accordingly, as used herein, a waste material may comprise all of these materials, alone or in combination, provided that it is in a form which is able to be combusted in a wet oxidation reactor. In the case of dry solid wastes it is understood that the addition of suitable solvents and the like would be required to enable such material to be in a liquid form or slurry when introduced into a reaction chamber in a reactor.
A 1995 study of Toxic Release inventory conducted by the U.S. Environmental Protection Agency (EPA) concluded that while the amount of toxic waste released into the environment is declining, the amount of toxic waste generated is increasing. In fact, the EPA has determined that industrial facilities generated 3% more toxic waste in 1995 than in 1994 and 7% more when compared to waste generated in 1991. In 1995, 2.2 billion pounds of waste were reported released into the air, water and land. While releases into air declined by about 7% from 1994 to 1995, discharges to water declined by about 10% and releases to land declined about 46% since 1988, releases into deep wells jumped by almost 20%. The EPA maintains that its Toxic Release inventory underscores the continuing need for pollution prevention and safe disposal of waste materials.
The need to safely dispose of waste materials, especially toxic and carcinogenic by-products of manufacturing and research processes, has commanded substantial public and government attention in the past two decades. Federal and state governments have responded to public pressure by adopting various statutes and regulations requiring that waste materials be managed and disposed properly with minimal risk to the public and the environment. Probably the most comprehensive and detailed plan for requiring safe management and disposal of hazardous waste is the federal Resource Conservation and Recovery Act of 1976 ("RCRA") as amended, and the regulations promulgated thereunder.
Despite continued efforts to accomplish safe waste disposal, a critical need remains for a means of disposing of waste. Many existing modes of waste disposal, i.e. landfills and surface impoundments, simply move hazardous substances from a high risk biosphere to a low risk biosphere. Many common disposal methods thus focus on isolating hazardous waste, rather than eliminating it. Alternatively, hazardous waste can be treated in an effort to eliminate or neutralize its hazardous characteristics. Treatments may be chemical or biochemical in nature, as in microbial biodegradation.
One solution to the problems inherent in waste disposal is to burn the waste with fuel using accelerated oxidation in specially devised reactors. Supercritical oxidation reactors use oxidizer mixtures, typically including water, at supercritical conditions to initiate a redox reaction with a fuel. Supercritical water is used in the oxidizer mix as the supercritical state of the mix accelerates the reaction and boosts reaction efficiency, thus minimizing unreacted (and therefore still harmful) exhaust.
In a water liquid/vapor phase diagram, there is a critical point of temperature (about 720.degree. F.) and a critical point of pressure (about 3,200 psia) above which there is only one single fluid phase. Although neither liquid nor vapor, this single fluid phase seems to have more of a vapor character than a liquid one. The single-phase condition occurring above the critical points is called supercritical condition.
It is worth noting that organic matter decomposes readily under supercritical conditions, and in the presence of oxygen, carbonaceous compounds oxidize completely to carbon dioxide, sulfur compounds mostly to SO.sub.3 and nitrogen compounds decompose mostly to molecular nitrogen. It is further worth noting that under supercritical water oxidation conditions, only small amounts of nitrogen oxide are produced, if any, in contrast with incineration which favors the production of nitrogen oxides.
However, as with the development of any new process or equipment, there are numerous limitations which have not been resolved, and which impair successful use and commercial exploitation. The use of extremely high pressures at elevated temperatures presents a serious problem in the construction of reactors. It is well known that as the temperature increases, the strength of materials decreases drastically. Supercritical pressures (greater than about 3,200 psia) at temperatures exceeding about 1,000.degree. F. present an enormous challenge to any construction material. In addition to the temperature/pressure challenge, a harsh environment exists inside the reactor. Moreover, these processes generate free radicals that are difficult if not impossible to control. Such free radicals can cause the metal in such specially constructed vessels to degenerate or become completely destroyed.
Thus there exists a need to improve the method and system for combusting and destroying combustible waste. There is a further need to improve the combustion of waste materials to reduce or eliminate the free radicals generated during such combustion.
Accordingly, a first objective of the present invention is to provide an improved waste destruction system for combusting and destroying organic and combustible wastes.
A further objective is to provide an improved waste destruction method and system wherein the organic and combustible waste is combusted and destroyed in an environment that may be less than, equal to, or greater than critical conditions, i.e., subcritical, critical or supercritical.
Another objective is to provide an improved waste destruction method and system wherein the amount of free radicals produced during the combustion and destruction of the organic and combustible waste is significantly reduced or even eliminated entirely.
Yet a further objective is to provide an improved waste destruction method and system wherein the corrosion inside the reaction chamber is significantly reduced or eliminated.